The present invention relates generally to spreaders or lifting beams and more particularly to an expandable spreader capable of being utilized for lifting containers of different sizes.
In recent years, considerable emphasis has been directed towards development of units that can be utilized for moving containerized cargo in dock and railroad areas. The most common type of unit that has been utilized for this purpose consists of some type of U-shaped frame which defines an open cargo container bay and the unit is usually self-propelled so that it can be manipulated to place a container in the bay area. This type of unit or straddle carrier conventionally has a spreader located within the bay area which can be raised and lowered and the container has corner fittings or castings having apertures of standard design with the spreader having latching mechanisms at the four corners thereof which are received into the apertures in the castings and secured therein so that the containers can be lifted and transported.
In the past few years, the sizes of containers have become fairly standard. Usually, the containers are 8 feet high and 8 feet wide and the most common lengths have been 20 or 40 feet. However, there are some containers of intermediate lengths, such as 30 or 35 feet and a few containers of various other intermediate lengths.
Since it is extremely critical to maintain the longitudinal spacing between the latching mechanisms on the spreader, it has become fairly common to have the spreader designed for the minimum length containers and to attach sub-frames of fixed lengths with latching mechanisms to the spreader to accommodate the other container lengths. However, this is very costly and requires considerable time to make all of the mechanical, hydraulic and electrical connections when a conversion is necessary.
In order to overcome this problem, numerous expandable spreaders have been proposed. One type of expandable spreader that has been proposed consists of a base section and expandable sections with latching mechanisms supported on the expandable sections.
When using two expansible spreader sections supported on a base section, for various reasons, the two extensible sections should be extended in approximately equal increments at the same time. Heretofore, this has been accomplished with rather complicated mechanisms such as motors with synchronized drive mechanisms for the respective sections or a rack and pinion interconnection between the base section and the expandable sections. Another proposed solution is to use plural cylinder and piston rod assemblies as the extension and retraction mechanism.
While such proposed synchronizing mechanisms may be acceptable for performing the intended function, the mechanisms heretofore proposed are rather complicated and add substantially to the overall cost of the spreader.